#29262: Custom Left Outer Join in Queries
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Reporter: Sassan Haradji | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version:
(models, ORM) |
Severity: Normal | Resolution:
Keywords: ORM Join | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Hugo Maingonnat):
I also need a way to generate a query with custom a join:
{{{
SELECT "main_table"."id" FROM "main_table" LEFT JOIN (SELECT
distinct(main_id) FROM through_table WHERE other_id = 14) as foo ON
foo.main_id=main_table.id ORDER BY "main_table"."id" DESC LIMIT 1;
}}}
The main queryset is generated by the view, and the left join subquery is
a custom django-filter. Using a `id__in` would work but I have to repeat
the ORDER BY DESC and LIMIT 1 in the subquery (otherwise it gets really
ineficient) and ideally the filter should be independant from the initial
queryset (so it does not know the ordering and limit). Also django-filter
needs to keep a queryset so I cannot generate a RawQueryset (I am not even
sure this is doable).
Having a `join` keyword in the extra function would have unlocked me.
The FilteredRelation object is only limited to a condition (q object) and
not a full SELECT query. If it could take a RawSQL or a queryset it would
be perfect.
So it looks like I cannot generate a quite simple query using any of the
django function, a bit frustrating :(
Like @Alexandr Artemyev I found out the CustomJoin trick but it looks very
brittle.
Hope my feedback will help understanding the issue :)
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Ticket URL: <https://code.djangoproject.com/ticket/29262#comment:18>
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